Burner control system

Abstract: In a fuel valve and ignitor control system the pull-in current for a fuel valve (16) operating on rectified alternating current is supplied through a normally open contact (r21) of a relay (R2) which is connected in series with a normally open contact (r11) of another relay (R1) and an intermittently operating hot surface ignitor (20). A normally closed contact (r12) of the other relay (R1) is connected in series with the ignitor (20) and the fuel valve (16) through a holding resistor (25), whereby actuation of the other relay (R1) provides unrectified alternating current to the ignitor (20) and actuates the first mentioned relay (R2) to provide pull-in current to the fuel valve (16). Deactivation of the other relay (R1) provides a holding current to the fuel valve (16) via the ignitor (20).

Description: The present invention relates generally to a control apparatus for fuel burners having an intermittent pilot and a hot surface ignitor, and more particularly to an arrangement of such apparatus in which energization of a fuel valve is conditioned on flow of electric current through the ignitor. For reasons set forth in detail in a number of prior references, including U.S. Patents 5,020,988, 5,035,607 and 5,133,656, a gas burner system employing an intermittently operating pilot ignited by a hot surface ignitor has become a preferred burner system arrangement. One safety concern with such an arrangement is that fuel gas must not be supplied to the burner if the ignitor is not operating properly. A variety of approaches have been taken to addressing this concern. For example, in the burner control system of U.S. Patent 5,020,988, fuel valve energization is controlled by a circuit, including a sequencer which locks out energization to a pilot valve, and, in turn, prevents energization of a main valve where attempts to light a pilot burner have been unsuccessful. U.S. Patent 5,035,607 discloses a burner control system in which ignitor voltage and/or current are monitored to indicate operating state of the ignitor, and used to prevent energization of the fuel valve in the event proper ignitor operation is not indicated. In both of the previously described arrangements, safety is ensured by sensing a condition related to proper ignitor operation, and utilizing the sensed condition to control a fuel valve operator. Each of these arrangements utilizes a flame sensor for detecting presence of a pilot flame, which condition implies proper operation of the ignitor. Detection of a pilot flame also causes power to be cut to the ignitor to prolong ignitor life, and causes opening of a main fuel valve. The arrangement of U.S. Patent 5,035,607 also implies proper operation of the ignitor from sensed voltage and current conditions at the ignitor, and does not allow fuel to be supplied to the pilot or main burners in the absence of predetermined voltage and/or current conditions, which provides additional safety. A more direct and simple arrangement for preventing supply of fuel to a burner if the ignitor is not operating properly, is to connect the fuel valve solenoid and ignitor in series so that the same current energizes both the ignitor and fuel valve. Thus, any condition which interferes with adequate current through the ignitor, such as the ignitor burning open, also prevents operation of the fuel valve. Such a system is shown in U.S. Patent 5,133,656. However, the arrangement disclosed in this patent is only suitable for a single fuel valve, and not to a dual fuel valve for use in a burner configuration including both pilot and main burners. US-A 3 432 246 describes an electrical flame ignition and supervising apparatus comprising the features listed in the preamble of claim 1. In a first embodiment of this known apparatus the fuel valve solenoid is energized via the contacts of a relay which simultaneously has further contacts for energizing the igniter. This relay requires a first predetermined electrical current for its actuation and requires a second smaller current for holding the solenoid valve open with simultaneously switching off the igniter. In a second embodiment a single solenoid operates the fuel valve as well as two sets of relay contacts with one of them being inserted into the energizing circuit for the igniter. In this case said relay has a particular structure for permitting the combined function of an energizing solenoid for the fuel valve and the energizing coil of a relay operating said contacts. The invention as characterized in claim 1 provides a burner control system with continuous check of hot surface ignitor during run cycle. Preferred details are described in the dependent claims. The invention incorporates a safety feature similar to that of U.S. Patent 5,133,656 into a dual fuel valve system, thus providing simplicity and direct fuel valve safety control in an intermittent pilot type fuel burner. The invention is an ignitor and fuel valve control for intermittent pilot burner apparatus, in which a first solenoid operated fuel valve requires greater current for pull-in than for holding in an actuated state, the pull-in and holding currents being supplied through separate current paths, of which the pull-in current path does not include the ignitor and the holding current path includes the ignitor. The coil of a first relay and pair of normally open pair of contacts of a second relay are connected in series with the ignitor across power supply terminals. A normally open pair of contacts of the first relay is connected to permit full power supply voltage to be applied across the fuel valve solenoid to provide adequate pull-in current. A normally closed pair of contacts of the second relay is connected between the ignitor and the fuel valve solenoid to permit holding current to be supplied to the fuel valve solenoid through the ignitor. The holding current path may include an impedance element to maintain current through that path at a value between the pull-in and holding current values of the fuel valve solenoid. A second solenoid operated fuel valve connected be supplied with current through a normally closed pair of contacts of the first relay may also be included. The second relay, as well as an electronic switch in the current path for the second fuel valve, may be controlled through a flame sensing and safe start check circuit in response to a call for burner operation. The invention will be described with reference to preferred embodiments shown in the drawing. Therein: Figure 1 is a simplified diagram of the applicants' control system, illustrating its principle operating concepts and functions; and Figure 2 is a more detailed illustration of the control system of Figure 1, partially in block diagram form. In a simplified illustration of Figure 1, reference numerals 11 and 12 identify power supply terminals for receiving alternating current at a predetermined voltage, typically 24 volts, and supplying the current to circuitry in the control system. Terminal 11 may be maintained at system ground potential. Reference numeral 13 identifies a thermostatic switch which may be a temperature sensitive bimetallic device located in a space whose temperature is to be controlled. Switch 13 is open when there is no demand for heat in the space. Upon a call for heat, switch 13 closes to supply the voltage from terminal 12 to a conductor 14 downstream from the switch. A coil of a first relay R1 is connected between conductor 14 and terminal 11. Also connected in series between conductor 14 and terminal 11 is a solenoid operated fuel valve 16, shown in block diagram form, and a normally open pair of contacts r21 of a second relay R2. Valve 16 may be a conventional commercially available fuel valve, as further discussed in conjunction with Figure 2. For purposes of the present invention, a significant characteristic of valve 16 is that the operating solenoid therein requires greater pull-in current for opening the fuel valve than holding current for maintaining the fuel valve in an open state. Connected in series between power supply terminals 11 and 12 are a conventional commercially available hot surface ignitor 20, a normally open pair of contacts r11 of the first relay R1 and a coil of the second relay R2. As shown, fuel valve 16 and normally open contact pair r21 are connected at a first junction 23, and ignitor 20 and normally open contact pair r11 are connected at a second junction 24. Connected in series between junctions 23 and 24 are an impedance element or resistor 25 and a normally closed pair of contacts r12 of the first relay R1. Resistor 25 is selected to have a value which, when thermostatic switch 13 and normally closed contact pair r12 are closed, maintains the current through the solenoid of valve 16 to a value between the pull-in and holding current values thereof. In operation, upon a call for heat, switch 13 closes, thus energizing coil R1 of the first relay. This causes normally open contact pair r11 to close, thereby energizing ignitor 20 and coil R2 of the second relay, and opening normally closed contact pair r12. Energization of coil R2 causes normally open contact pair r21 to close, thereby supplying pull-in current to valve 16, which supplies fuel to a burner (not shown) proximate energized ignitor 20 which ignites the fuel. Flame sensor apparatus which detects flame at the burner, as further described in conjunction with Figure 2, and circuitry associated therewith, then de-energizes the first relay R1, which causes contact pair r11 to open and contact pair r12 to close. This terminates the application of substantially full power supply voltage to ignitor 20, thereby rendering the ignitor incapable of normal operation, and de-energizes coil R2, thereby opening contact pair r21 which terminates application of full power supply voltage to valve 16. However, holding current for valve 16 is now supplied through a second current path including ignitor 20, contact pair r12 and resistor 25 to maintain valve 16 in an open state as long as thermostatic switch 13 is closed. As is apparent from the foregoing description, ignitor 20 must be capable of conducting current in order for valve 16 to be energized. Any condition which precludes current flow through ignitor 20, such as the ignitor having burned open, prevents both pull-in and holding current from being supplied to valve 16. Pull-in current is prevented because electrical continuity of ignitor 20 is required for actuation of the second relay and closure of contact pair r21. Holding current is prevented because any holding current is supplied only through ignitor 20. Accordingly, the system of Figure 1 provides a very simple and direct implementation for preventing opening of valve 16 if ignitor 20 is not capable of normal operation. In the more detailed illustration of the applicants' ignitor and fuel valve control system shown in Figure 2, the same reference numerals as in Figure 1 are used to identify like elements. Figure 2 also illustrates a conventional fuel burner assembly 30, which may include both pilot and main burners supplied with fuel as indicated by dashed line 31 from valve 16. Valve 16 is shown as dual fuel valve, of which a pilot valve is operated by a solenoid 32 and a main valve is operated by a solenoid 33. The arrangement of valve 16 is such that fuel to the pilot burner is supplied through the pilot valve alone, and fuel to the main burner is supplied from the pilot valve through the main valve. Solenoid 32 is shown as connected in a full-wave diode bridge so as to be supplied with full-wave rectified alternating current, which is a conventional implementation for a solenoid operator requiring greater pull-in current than holding current. Solenoid 33 is connected to be supplied with half-wave rectified alternating current through a diode 34. A diode 35 connected across coil 33 provides a current circulation path through the coil during the portions of a current cycle when diode 34 is reverse biased. Coil 33 and diode 34 are connected in series with a normally closed pair of contacts r22 of the second relay R2 and a bidirectional electronic switch or triac 41, between terminal 11 and conductor 14. A relatively constant DC voltage is produced by voltage regulation circuitry 42 connected between terminal 11 and conductor 14, and is supplied to other portions of the circuit requiring a DC supply voltage. Reference numeral 43 identifies a commercially available hybrid circuit for performing certain conventional sensing, sequencing and control functions. Specifically, circuit 43 includes a relay driver 44 which supplies suitable energization to coil R1 of the first relay. Circuit 43 also includes a flame sensor circuit 45 to which is connected a flame probe 46 positioned relative to burner assembly 30 so as to detect flame produced particularly by the pilot burner, and which, under predetermined conditions, supplies an electrical control signal to electronic switch 41 over a conductor 47. Hybrid circuit 43 also includes safe start circuitry 48 which performs certain logic and sequencing functions. In particular, at the beginning of an operating cycle, circuit 48 checks to ensure that no flame is detected or indicated by flame sensor circuit 45 before activating relay driver 44. Coil R2 of the second relay is shown enclosed in a dashed line box 50 which may contain supplemental circuit components to carry a portion of the current required for full operation of ignitor 20, thereby avoiding a requirement that all of the current be carried through coil R2. Although relays with AC coils capable of carrying the required current are commercially available, additional components, as indicated by box 50, can be provided to permit the use of a less expensive relay. The operation of the system of Figure 2 is similar to that described in conjunction with Figure 1. In particular, upon a call for heat in the space in which thermostatic switch 13 is located, the switch closes, thereby applying voltage to conductor 14. The voltage on conductor 14 is supplied to fuel valve solenoid coil 32 and its surrounding diode bridge, triac 41 and hybrid circuit 43. As previously described, if safe start circuit 48 determines that conditions are satisfactory for burner start up, it activates relay driver 44 which energizes relay coil R1 and closes normally opened contact pair r11 to energize ignitor 20 and relay coil R2. Energization of relay coil R2 closes contact pair r21 to supply pull-in current to pilot valve solenoid 32, thereby causing fuel to be supplied to the pilot burner of burner assembly 30. The pilot burner is ignited by energized ignitor 20, and the pilot flame is detected by flame probe 46, which causes flame sensor circuit 45, in conjunction with safe start circuit 48, to supply a control signal to triac 41 through which energization current may be supplied to main valve solenoid 33. After sensing a pilot flame, flame sensor circuit 45, in conjunction with safe start circuit 48, deactivates relay driver 44, thereby opening contact pair r11. This removes the full power supply voltage from ignitor 20 and de-energizes relay coil R2, thereby opening contact pair r21 through which pull-in current was supplied to pilot valve solenoid 32 and closing contact pair r22.. De-energization of relay coil R1 also causes contact pair r12 to close, thereby maintaining holding current to pilot valve solenoid 32 through ignitor 20, resistor 25 and contact pair r12, as long as thermostatic switch 13 is closed. As previously described in conjunction with Figure 1, both pull-in and holding current to pilot valve solenoid 32 depend on electrical continuity through ignitor 20. In particular, current for energizing relay coil R2, whose related normally open contacts r21 supply pull-in current to solenoid coil 32, must pass through ignitor 20. In addition, holding current through solenoid coil 32 must pass through ignitor 20. Thus, electrical continuity of ignitor 20 is continuously checked during the burner run cycle, and no fuel can be supplied to the burner if the ignitor is not in operating condition. Ignitor 20 in Figure 2 is initially energized by alternating current supplied to power supply therminals 11, 12. Both solenoids 32, 30 are supplied with direct curent, and the reduced holding current through coil 32 maintains ignitor 20 energized when relay contact r11 opens alter a flame is sensed by sensor 46 causing relay 21 to drop out.

Claims: A fuel valve control system comprising: a) a solenoid operated fuel valve (16) requiring a first predetermined electric current for actuation and requiring a second smaller predetermined current for holding the valve in the actuated state; b) a resistive ignitor (20) connected into the pull-in circuitry (R2, r11, 20) for the fuel valve solenoid (16) as well as into the holding circuitry (25, r12, 20) of said solenoid; c) a temperature-responsive switch (13); d) power supply terminals (11, 12) for supplying electrical energy to the control system; and e) a first relay (R1); characterized in that : f) said first relay (R1) is connected in series with said switch (13) across said power supply terminals; g) a second relay (R2) is connected in series with said ignitor (20) and a normally open contact (rll) of said first relay (R1) across said power supply terminals (11, 12); h) said valve (16) is connected in series with a normally open contact (r21) of said second relay (R2) in parallel to said first relay (R1); i) an impedance element (25) and a normally closed contact (r12) of said first relay (R1) are connected in series between a first junction (23) on the line connecting said valve (16) to said normally open contact (r21) of the second relay (R2) and a second junction (24) on the line connecting said ignitor (20) to said normally open contact (r11) of said first relay (R1) and to said second relay (R2). The system of claim 1, characterized in that said impedance element, preferably a resistor (25), has an impedance value which limits the current flowing therethrough to a value less than said first predetermined current but greater than said second predetermined current. The system of claim 1 or 2, characterized in that the ignitor (20) is an intermittently operating hot surface ignitor and the power supply terminals (11, 12) are supplied with an alternating electric current (AC). The system according to one of the claims 1 to 3, characterized in that a) said fuel valve (16) includes a first solenoid (32) controlling a valve in the fuel supply line to a pilot burner and further includes a second solenoid (33) controlling a valve in the fuel supply line to a main burner; b) a flame sensor circuit (46, 43) monitoring said pilot burner controls an electronic switch (41) which is connected in series with said second solenoid (33) and a normally closed contact (r22) of said second relay (R2), which series circuit is connected in parallel to another series circuit including the first solenoid (32) and the normally open contact (r21) of the second relay (R2); wherein c) the flame-sensing circuit (46, 43) is operable to supply electric current to the first relay (R1) only if no flame is detected at the burner (30), and is operable to supply an electric control signal to said electronic switch (41) only if a flame is detected at the burner. The system of claim 4, characterized in that the flame-sensing circuit (43, 46) includes: a) a relay driver circut (44) for the first relay (R1); b) said flame sensor circuit (45) having its input connected to a flame sensor (46); c) a safe start circuit (48) connected between said flame sensor circuit (45) and said relay driver (44). The system of claim 4 or 5, characterized in that a) said first solenoid (32) is connected into the diagonal branch of a rectifier bridge whose input terminals are connected to the temperature-responsive switch (13) and the normally open contact (r21) of the second relay (R2), respectively; and b) said second solenoid (33) is connected in series with a diode (34) between said electronic switch (41) and the normally closed contact (r22) of the second relay (R2). The system of claim 1, characterized by : a) a control terminal (14), a fuel valve energization terminal (23), and an ignitor energization terminal (24); b) said first electrical relay (R1) having a normally open contact (r11), a normally closed contact (r12) and a coil (R1); c) said second electrical relay (R2) having a normally open contact (r21) connected between said first power supply terminal (11) and said valve energization terminal (23); d) first electrical connecting means connecting the coil of said second electrical relay (R2) and the normally open contact (r11) of said first relay (R1) in series between said second power supply terminal (12) and said ignitor energization terminal (24); e) second electrical connecting means (25) connecting the normally closed contact (r12) of said first relay (R1) between said valve energization terminal (23) and said ignitor energization terminal (24); and f) third electrical connecting means connecting the coil (R1) of said first relay between said second power supply terminal (11) and said control terminal (14). The system of claim 7, characterized in that said second electrical connecting means includes an impedance element (25) for limiting electric current flowing through the solenoid coil (32) of a fuel valve (16) connected to the valve energization terminal (23) and through the ignitor (20) connected to the ignitor energization terminal (24) to less than the pull-in current of the solenoid coil (32).

Inventors: BOHAN JOHN E JR, PERSCHBACHER VICKI L, PETERSON SCOTT M, BOHAN, JOHN E JR, PERSCHBACHER, VICKI L, PETERSON, SCOTT M
Applicants: HONEYWELL BV, HONEYWELL B.V.
Application year: 1994
Main classification: F23N5
IPC codes: F23N5